1. Field of the Invention
The present invention relates to a linear actuator, and more particularly, to a linear actuator having a small size and a light weight.
2. Description of the Related Art
An actuator is demanded to have a good responsibility, a large output, a large displacement, a good position maintainability, a reproducibility and a good efficiency. A solid displacement type actuator using piezoelectric property, electrostriction or super magnetostriction has good responsibility and large output. However, because the solid displacement type actuator has a small displacement is made of fragile material, the solidity and stiffness are low.
Thermal shape memory alloy has a large output and a large displacement. However, the thermal shape memory alloy has a hysteresis characteristic in the displacement and the position maintainabily is low. Also, the responsibility is remarkably low and the efficiency is low.
A rotation type electromagnetic motor has a good responsibility and a large output. Also, the electromagnetic motor has a large displacement, a good position maintainability and a good solidity. Thus, the electromagnetic motor has a good efficiency. However, the electromagnetic motor has no linearity and requires an external conversion mechanism for converting a rotation operation into a linear operation. Further, the electromagnetic motor requires a deceleration mechanism. Therefore, it is difficult to miniaturize the motor.
An electromagnetic linear motor does not require such a mechanical system. However, the electromagnetic linear motor has a small output, and requires a feedback control system for position maintainability so that an application field is limited. Because electromagnetic force does not act stably to a magnetic substance body, a feedback control is necessarily required in the actuator using electromagnetic force.
An actuator using fluid pressure is complicated in an oil leakage measure and a fluid route is complicated because the actuator contains many valves.
Linear drive is needed for a joint of an arm or finger of a robot, in addition to rotation drive. A small rotary motor having a large output is generally used for the linear drive. The rotary motor is good in all physical characteristics as mentioned above. However, large size units such as the deceleration mechanism and the external conversion system need to be added in narrow spaces such as the finger and the arm, so that the rotary motor must be made to have a small size. As a result, the output of the rotary motor becomes small.
A technique is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 8-214530), in which a linear motor type actuator is fabricated using a coil. In the actuator, magnetic flux convergence is improved so that a magnetic flux uniformly passes through a yoke. Thus, armature reaction effectively operates over the entire stroke. As a result, the space saving is made possible.
In the field of a finger and a joint of a robot, an electromagnetic motor is demanded to have physical and mechanical characteristics such as (1) a large output, (2) a good responsibility, (3) a large displacement and (4) a good reproducibility characteristics, (5) a good efficiency, (6) a large output, (7) a small size, and (8) a high linearity. In addition, the high degrees of freedom of the design are demanded. Both of these physical and mechanical characteristics are demanded in the industry field such as an industrial robot, a machine tool, and a car. In such an application field of the linear actuator, the small size and light weight are especially demanded without use of any displacement convert mechanism and deceleration mechanism.
An object of the present invention is to provide a linear actuator in which smallness and lightening can be more promoted by mixing and combining the physical characteristics and the mechanical characteristics.
Another object of the present invention is provide a linear actuator in which degrees of freedom of design can be made higher by mixing and combining the physical characteristics and the mechanical characteristics.
Still another object of the present invention is to provide a linear actuator in which reproducibility and responsibility can be made higher so that smallness and lightening can be more promoted by mixing and combining the physical characteristics and the mechanical characteristics.
Yet still another object of the present invention is to provide a linear actuator in which deformation expanding mechanism and operation conversion mechanism are not necessitated and smallness and lightening can be more promoted by mixing and combining the physical characteristics and the mechanical characteristics.
In an aspect of the present invention, a linear actuator includes a supporting unit with a stopper, a linear output unit, a movable unit, and a magnetic flux generating unit. The movable unit is connected to the stopper of the supporting unit at one end of the movable unit and to the linear output unit at the other end thereof. The magnetic flux generating unit generates first magnetic fluxes. The movable unit has elasticity, and expands or contracts based on action of said first magnetic fluxes and the elasticity. The linear output unit linearly moves in response to the expansion or contraction of the movable unit.
The movable unit desirably includes a spring coil.
Also, the magnetic flux generating unit may generate the first magnetic fluxes in a direction orthogonal to a direction of the second magnetic fluxes.
Also, at least a part of the magnetic flux generating unit is accommodated in the movable unit. In this case, the magnetic flux generating unit may include a bobbin case, and an electromagnetic coil which is wound on the bobbin case.
In this case, a control unit is further provided to supply current to the magnetic flux generating unit such that the magnetic flux generating unit generates the first magnetic fluxes.
When the movable unit is composed of a spring coil, the control unit may supplies a second current to said spring coil such that the spring coil generates second magnetic fluxes. The spring coil expands or contracts such that interaction between said first magnetic fluxes and said second magnetic fluxes balances with elasticity of said spring coil. In this case, the control unit may supply constant current to the movable unit and control the current supplied to the electromagnetic coil to control the expansion and contraction of the movable unit. Alternatively, the control unit may supply constant current to the magnetic flux generating unit and control the current supplied to the movable unit to control the expansion and contraction of the movable unit.
Also, the magnetic flux generating unit may include a bobbin case and magnets which are embedded in the bobbin case. When the movable unit is composed of a spring coil, a control unit is further provided to supply a second current to said spring coil such that said spring coil generates second magnetic fluxes. The spring coil expands or contracts such that interaction between said first magnetic fluxes and said second magnetic fluxes balances with elasticity of said spring coil. In this case, the control unit may control the current supplied to the movable unit to control the expansion and contraction of the movable unit.
Also, the supporting unit may include a first pipe and the stopper which is attached to one end of the first pipe. A part of the linear output unit is slidably accommodated in the first pipe. In this case, the linear output unit may include a second pipe provided to be slidable with the first pipe, and a stopper which is attached to one end of the second pipe opposing to the first pipe and to which the movable unit is connected.
Also, the supporting unit may include a first pipe, the stopper which is attached to one end of the first pipe, and an additional stopper which is attached to the other end of the first pipe and has a hole section. A part of the linear output unit is slidably accommodated in the first pipe. In this case, the linear output unit may include a base section which is accommodated in the first pipe and to which the movable unit is connected, and the moving section which extends from the base section through the hole section of the additional stopper.
Also, the stopper of the supporting unit and the magnetic flux generating unit may be made unitary.
In another aspect of the present invention, a linear actuator includes a magnetic flux generating section and a movable section. The magnetic flux generating section is fixed and generates first magnetic fluxes in a first direction. The movable section includes a spring coil, is attached to the magnetic flux generating section, accommodates at least a part of the magnetic flux generating section and generates second magnetic fluxes in a second direction orthogonal to the first direction. The movable section linearly expands or contracts such that interaction between the first magnetic fluxes and the second magnetic fluxes balances with the elasticity.
Here, the movable unit may include a spring coil. Also, the magnetic flux generating section may include a bobbin case and an electromagnetic coil which is wound on the bobbin case to generate the first magnetic fluxes.
Also, the movable unit may include a spring coil. Also, the magnetic flux generating section may include a bobbin case and magnets which are embedded in the bobbin case to generate the first magnetic fluxes.
Also, the magnetic flux generating section may include a first pipe and a stopper which is attached to one end of the first pipe. A part of the movable section is provided to be slidable with the magnetic flux generating section.
In still another aspect of the present invention, a linear actuator includes a mechanical operation body, a magnetic flux generating unit and a linear output body. The mechanical operation body expands or contracts in response to magnetic force. The magnetic flux generating unit generates magnetic fluxes in a direction orthogonal to a direction of expansion or contraction of the mechanical operation body. The linear output body outputs contraction power of both ends of the mechanical operation body and moves relatively to in the direction of the expansion or contraction of the mechanical operation body. The mechanical operation body has a spring constant and expands or contracts to a length corresponding to the magnetic flux generated by the magnetic flux generating unit.